The present invention relates to reforming catalysts comprising platinum on alumina, and preferably also comprising rhenium.
It is well known in the catalytic reforming of petroleum hydrocarbons in the presence of hydrogen, which reforming is frequently called hydroforming, that complex chemical reactions occur. Thus, when petroleum hydrocarbon fractions such as those boiling in the gasoline range, particularly between about pentane and 450.degree. F., are mixed with hydrogen and passed over a platinized alumina catalyst at a temperature of about 600.degree.-1100.degree. F. and pressure of about 25-500 psi, i.e., at reforming conditions, their fuel value in an internal combustion engine is materially improved. This is due to a number of reactions which take place simultaneously, including an isomerization reaction, dehydrocyclization and aromatization reactions and also a hydrocracking reaction.
Platinum-alumina reforming catalysts are often made by impregnating alumina with a platinum compound. For example, U.S. Pat. No. 3,617,519 discloses the preparation of a platinum-rhenium-alumina reforming catalyst wherein the platinum is impregnated into an alumina support by commingling the alumina support with an aqueous solution of chloroplatinic acid. Following the platinum impregnation, the impregnated carrier is typically dried and subjected to a conventional high temperature calcination or oxidation treatment.
U.S. Pat. No. 3,617,519 discloses that in most cases it is advantageous to adjust the concentration of the halogen component in the platinum-rhenium-alumina catalyst during the calcination step by injecting, into the air stream used therein, an aqueous solution of a suitable halogen-containing compound. U.S. Pat. No. 3,617,519 discloses that the halogen component can be added to the catalyst in various ways including adding the halogen during the impregnation through the utilization of a mixture of chloroplatinic acid and hydrogen chloride.
Typical calcination temperatures used in the preparation of the alumina support for reforming catalysts cover a wide range from about 800.degree. to 1300.degree. F., and frequently are 1100.degree. F. or lower.